From my point of view, and based on the tests I have done, for the full screen format to be useful, we need to solve at least two very important things first:
1. That the canvas in which the blocks are inserted also occupies the width of the screen. This would be extremely useful for working with groups of blocks, especially when they include multiple columns to which text must be added. If the full screen leaves a canvas just as small as previously anchored in the center of the screen, what's the point?

Replace the upper left button (arrow) so that the administration menu reappears instead of taking you to the list of entries, which does not make any sense in the editor.
By inertia, the user is used to collapsing the admin panel and customizer menus and redisplaying them by clicking an arrow they expect to find ...

I really think that those in charge of programming do not use the block editor too much in their day to day ... they are obvious things that they leave behind while they want to advance in other functions that are not so necessary yet.